Liquid crystal displays (LCDs) including black matrices are known in the art. For example, see U.S. Pat. Nos. 5,666,177; 5,682,211; and 5,641,974, the disclosures of which are hereby incorporated herein by reference.
The purpose of black matrices in LCDS is to block light that is extraneous to the display or pixels thereof that would otherwise emerge on the viewing side of the display, and reduce overall contrast. Thus, in order to achieve satisfactory contrast in high ambient light conditions in LCDs, black matrices (BMs) are provided, and must be able to absorb and reflect light. Black matrices are often located on the color filter substrate and function to prevent ambient light surrounding the display from reducing display contrast, and to efficiently do this, reflection of light off of the black matrix must be kept to a minimum. A number of materials have been conventionally used for black matrix applications, include CrO.sub.x and Cr combinations, black polymer, black polyimide, SiO.sub.x and Si combinations, and Si-rich SiN.sub.x.
Unfortunately, conventional black matrix materials discussed above suffer from at least the following problems: (1) reflection is not low enough for certain display applications (e.g. CrO.sub.x /Cr, black polymer or polyimide, Si-rich SiN.sub.x) as these materials provide reflection of light in the range of from about 1.5 to 7.0% (i.e. this is too high of a reflection for certain LCD applications); (2) some of these materials experience difficulties in patterning and/or etching (e.g. polyimide, CrO.sub.x /Cr); and/or (3) they are very expensive (e.g. e-beam evaporated SiO.sub.x /Si from Optical Coating Lab., Inc.).
It has been found that for low reflection to be achieved, it is desirable to substantially match indices of refraction between black matrix layers at least at interfaces defined thereby with the substrate upon which they are provided. Silicon dioxide has an index of refraction substantially matched (i.e. very close) to glass, however, its index does not substantially match with a-Si film which is typically used with silicon dioxide in black matric applications. Also, PECVD silicon nitride typically has a refractive index between 1.8 and 2.2, and it thus does not always substantially match with glass (glass has a refractive index of about 1.5). These, of course, are problematic, as lack of proximity of adjacent refractive indices can cause reflection.
It is apparent from the above that there exists a need in the art for an improved black matrix system/material, and method of making same, for display (e.g. LCD) applications. It would be desired if improved reflectivity characteristics and/or manufacturability could be achieved.
It is a purpose of this invention to fulfill the above-described needs in the art, as well as other needs which will become apparent to the skilled artisan from the following detailed description of this invention.